1. Field of the Invention
The present claimed invention relates to an apparatus of measuring particulate matters that measures the mass of particulate matters contained in exhaust gas of an engine.
2. Background Art
A filter mass method is well known as a method of measuring the mass of particulate matters as being one of emission matters from an engine. The filter mass method is a method to collect the particulate matters by arranging a collecting filter on a flow channel of exhaust gas from an engine so as to measure the mass of the particulate matters by means of a balance or the like. Since it is possible for this method to directly measure the mass of the particulate matters practically having no standard substance whose properties can be specified, certainty and accuracy of measurement can be expected. As a result, a constant volume sampler (CVS) that analyzes all amount of the exhaust gas from the engine after the exhaust gas is diluted is used on a standard basis for current emission gas test among measurement apparatuses using the filter mass method.
Meanwhile, recently there is a request for measuring a time series variation of the emitted amount of the particulate matters while the vehicle is dynamically running on a road with the view of further improvement of engine performance or environmental issues. However, since the filter mass method is, so called, a measurement method of a batch type by which only accumulated mass of the particulate matters emitted during a certain period is measured, it is not possible to learn how the mass of the particulate matters varies from moment to moment in accordance with a dynamic driving situation.
Then as an alternative for the filter mass method, a flame ionization detector (FID), an electric low pressure impactor (ELPI), a scanning mobility particle sizer (SMPS) or a diffusion charger sensor (DCS) that can continuously measure the particulate matters on a real time basis has been presented and developed. The flame ionization detector is to measure a number of carbon atoms contained in sample gas, and the electric low pressure impactor and the scanning mobility particle sizer are to count a number of particles. The diffusion charger sensor is an apparatus to electrically charge a surface of particles and to measure its electrically charged amount.
In accordance with these apparatuses, it is possible to conduct measurement also while the vehicle is running on a road. However, these apparatuses measure a number of carbon atoms, a number of particulate matters or a surface area of particulate matters and do not directly measure the mass of the particulate matters. As a result, in order to obtain the mass of the particulate matters from a measurement result, it is necessary to obtain a correlation with the measurement result by the collecting filter measurement method under the same condition and to calculate the mass of the particulate matters based on the correlation.
Then it can be conceived that a correlation between the measurement result by the filter mass method and the measurement result by the electric low pressure impactor method in each driving state of the engine is obtained in advance and then the dynamic variation of the mass of the particulate matters is calculated by applying the correlation to the measurement result by the electric low pressure impactor at a time when the vehicle is running on a road.
However, since the correlation is eventually a correlation at a time when each driving state of the engine is kept at a certain static state, it is unreasonable to apply this correlation to a dynamic state wherein the vehicle is running on a road and to extrapolate the actual dynamic variation of the mass of the particulate matters.
Background information may be found in WIPO International Publication No. WO 2004/046517 A2.